1. Field of the Invention
The invention relates to a fuel injection device for internal combustion engines, in particular a common rail injector, with a housing that has an injection end, with a recess provided in the housing, with at least one axially movable valve element, which is disposed in the recess and which cooperates with a valve seat, and has a pressure surface oriented away from the injection end, which pressure surface axially delimits a control chamber, with a device that acts on the valve element counter to the force resultant of the pressure surface, and with a control valve that is connected to the control chamber via a flow throttle.
2. Description of the Prior Art
A known fuel injection device of the kind described above is on the market. It is a common rail injector. In it, an axial end face of a valve needle delimits the control chamber. A sleeve part, which has an inlet throttle in its wall, delimits the control chamber radially. A housing part that contains an outlet throttle delimits the control chamber on the side opposite from the valve needle. The inlet throttle is connected to a high-pressure supply, whereas the outlet throttle is connected to a low-pressure region via a control valve. The throttle action of the inlet throttle is more powerful than that of the outlet throttle.
The normal high fluid pressure prevails against the pressure surface of the valve needle, whose force resultant points in the opposite direction from the axial end surface of the valve needle. In order to lift the valve needle up from its valve seat in the vicinity of the injection end, the pressure in the control chamber is reduced by an appropriate switching of the control valve. A sufficient pressure difference generates a resultant force that lifts the valve needle up from its valve seat.
The object of the current invention is to modify a fuel injection device of the type mentioned at the beginning so that it has a particularly simple design.
This object is attained in a fuel injection device of the type mentioned at the beginning by virtue of the fact that the on-off valve has at least three connections and at least two switching positions and is connected to a high-pressure fluid inlet and a low-pressure fluid outlet on the one side and is connected to the flow throttle on the other side.
In the fuel injection device according to the invention, therefore, only one flow throttle is required. It functions as an inlet throttle in the one direction and functions as an outlet throttle in the other direction. On the whole, the fuel injection device according the invention requires fewer flow conduits, which simplifies its design and reduces its production costs. In addition, the fuel injection device designed in this way can also be embodied in a smaller form.
Advantageous modifications of the invention are also disclosed.
In a first modification, the flow throttle is embodied so that its throttle action in the direction toward the on-off valve is more powerful than in direction toward the control chamber. Therefore the control chamber empties more slowly than it refills. This in turn means that the fuel injection device opens more slowly than it closes. An opening and closing behavior of this kind is favorable for the mixture formation in the combustion chamber of the engine.
One simple possibility for embodying the directionally dependent throttle action is comprised in that the flow throttle has a trumpet-shaped enlargement at each of its ends and the curvature and/or the curvature progression of the trumpet-shaped enlargement of the one end differs from that of the other end.
It is particularly preferable if the trumpet-shaped enlargement at the end of the flow throttle oriented toward the control chamber is more sharply curved than the enlargement at the end oriented toward the control valve.
Alternatively or in addition, the flow throttle can also be embodied so that when fluid flows out of the control chamber, cavitation occurs downstream of the flow throttle. A cavitation of this kind increases the flow resistance when fluid flows out of the control chamber toward the control valve, which increases the pressure drop that occurs due to the flow throttle. This in turn reduces the pressure on the side of the control valve oriented toward the flow throttle. This consequently reduces the pressure drop that occurs due to the control valve itself, so that tolerances of the flow gap in the control valve have less of an impact. As a result, a simpler and less expensive control valve can be used.
In order to be able to generate such a cavitation, it is advantageous if the flow throttle has a conical form in the longitudinal direction, its cross-section at the end oriented toward the control chamber being smaller than at the end oriented toward the control valve.
The development of a cavitation can be intensified by the placement of a diffuser at the outlet of the flow throttle toward the control valve.
A particularly preferred embodiment is the fuel injection device in which the control valve has a piezoelectric actuator. Such a piezoelectric actuator works very rapidly.
A particularly preferred modification of the fuel injection device according to the invention is distinguished by the fact that it has at least one second flow throttle, which continuously connects the control chamber to the high-pressure fluid inlet, the throttle action of the second flow throttle being more powerful than that of the first flow throttle in a direction from the control chamber toward the control valve. With this fuel injection device, an additional machining step is in fact required in order to produce the second flow throttle, but this second flow throttle can accelerate the filling of the control chamber and can therefore considerably increase the closing speed of the valve element.
The invention also proposes that the valve element be provided with a second pressure surface, whose force resultant is directed essentially counter to the force resultant of the first pressure surface and which delimits a pressure chamber that is connected to the high-pressure fluid inlet. Therefore, with this fuel injection device according to the invention, a force resulting from the exertion of a high pressure on a pressure surface of the valve element acts on the valve element in the opening direction. This means that no mechanical elements, for example springs etc., are required here to exert the force required to lift the valve element up from the valve seat. This has a positive impact on both the production costs and the service life of the fuel injection device.
In a modification that builds on this one, the invention proposes that the pressure chamber be connected to the high-pressure fluid inlet by means of a flow conduit let into the housing and that the second flow throttle branch from this flow conduit. The production of the fluid connection of the high-pressure fluid inlet via the second flow conduit and the second flow throttle is particularly simple to achieve.
The invention also relates to a fuel system with a fuel tank, with at least one fuel injection device, which injects the fuel directly into the combustion chamber of an internal combustion engine, with at least one high-pressure fuel pump, and with a fuel accumulation line to which the fuel injection device is connected.
In order to be able to manufacture a fuel system of this kind in a manner that is less expensive and simpler on the whole, the invention proposes that the fuel injection device be embodied in the manner mentioned above.
The invention also relates to an internal combustion engine with at least one combustion chamber into which the fuel is directly injected.
In order to keep the costs for this internal combustion engine as low as possible and to simplify the production and design, the invention proposes that the internal combustion engine have a fuel system of the type mentioned above.